Britain’s gone nine days with almost no wind generation, and forecasts show the calm conditions persisting for another two weeks.

The wind drought has pushed up day-ahead power prices to the highest level for the time of year for at least a decade. Apart from a surge expected around June 14, wind levels are forecast to stay low for the next fortnight, according to The Weather Company.

U.K. turbines can produce about as much power as 12 nuclear reactors when conditions are right. During the “Beast from the East” storm that hit Britain in March, they generated record levels of power and at times provided the biggest share of the nation’s electricity.

Luckily the current British wind drought occurred in Summer, but wind droughts can occur any time of year.

If countries like Britain go 100% renewable, its only a matter of time until a prolonged winter wind drought coincides with near zero solar energy availability, leading to weeks or even months without power at the coldest time of the year. Low wind conditions in Britain sometimes coincide with winter high pressure systems, which can be extremely cold.

No conceivable battery backup would bail a country out of a disaster like that.